1. Technical Field
The present disclosure relates to an antenna device including a plurality of antenna elements and an EBG (electromagnetic band gap) structure. The present disclosure also relates to a wireless communication apparatus including such an antenna device and a radar apparatus including such an antenna device.
2. Description of the Related Art
Conventionally, it has been known that in an antenna device including a plurality of antenna elements and communicating in a millimeter-wave band, an EBG structure is used to ensure isolation between the antenna elements (see Japanese Patents Nos. 4650302, 5112204, and 5212949) Since the EBG structure becomes higher in impedance at a predetermined frequency (antiresonant frequency), the antenna device including the EBG structure can enhance the isolation between the antenna elements at the frequency.
A known example of the EBG structure is one that includes mushroom conductors including a plurality of patch conductors formed on a dielectric substrate, a plurality of via conductors, and a grounded conductor. The performance of the mushroom EBG structure depends on the diameter of each of the via conductors, the minimum size of each of the patch conductors, and the like. When the size of the conventional EBG structure is optimized so that the isolation between the antenna elements in the EBG structure is enhanced, high isolation is achieved only in a limited frequency bandwidth. Therefore, the conventional EBG structure has difficulty in ensuring sufficiently high isolation across a wide frequency bandwidth.
Meanwhile, providing an additional component or the like to change the antiresonant frequency of the EBG structure causes an increase in size of the antenna device and also causes an increase in cost.